Going Viral: The Science of Coronavirus

Viruses are in the news. A new type of coronavirus that appeared in Wuhan, China, has stricken nearly 81,000 people in that country and been diagnosed in 108 countries, including the United States. According to the World Health Organization, this new virus, dubbed SARS-CoV-2, that causes the disease COVID-19 is now at the pandemic level, and public health resources are being mobilized to try to contain it.

But what exactly is a virus? Why is SARS-CoV-2 different from the virus that causes the common cold? DePaul Magazine spoke with Associate Professor Sarah Connolly, a herpesvirus researcher who teaches several courses in virology in DePaul’s College of Science of Health, about the nature of coronaviruses and other viruses, and how we can protect ourselves from infection.

Associate Professor Sarah Connolly

Sarah Connolly: There are coronaviruses that people get infected with all the time. I think it’s about 10% of the colds that we experience are caused by coronaviruses, but we recover from those. This coronavirus differs from those in that we have a 2–3% fatality rate right now. Also, this new coronavirus is newsworthy because it recently jumped into the human population, probably from some type of animal, and is now spreading between people. That doesn’t happen that often.

DePaul Magazine: From a biological standpoint, is there something really different about SARS-CoV-2 or is it just a matter of immunity levels or tolerance?

SC: It’s probably both, but I think there is something different about this virus. Many of the viruses that commonly infect people have co-evolved with people. Viruses that kill their hosts are not particularly successful viruses. A virus needs to be able to spread between hosts.

So this virus, through a random exposure between the animal that was infected and the human it infected, happens to be able to spread through humans. Why is this one deadly, whereas other viruses aren’t? I think it’s partly because of its recent introduction into the human population.

Our immune system can handle it, but for 2–3% of people, it overwhelms them. This is also true for the influenza virus. For example, the annual circulating strains of influenza have about 0.05% fatality rate. But SARS-CoV-2 is much more likely to be deadly than influenza.

DPM: Vaccines have gotten a bad rap in recent years. Do vaccines really help to prevent a viral infection?

SC: Absolutely. The CDC reported that the flu vaccine was 29% effective in the 2018–19 flu season. That sounds low, but it’s better than nothing, and the vaccine has been demonstrated to be safe.

I was just talking to a colleague about why coronavirus is such a big deal in the news. We were thinking about how my generation—I’m 44—hasn’t really had to worry about infectious disease. Polio is not a thing that I ever had to worry about. I never had to worry about measles either.

People talk about vaccines being a victim of their own success. People are not worried. They say, ‘What’s the big deal with measles?’ But measles kills one out of a thousand people, so I don’t want it.

The reason I don’t have to worry about polio or measles viruses is because of vaccines. When these outbreaks of Ebola or coronavirus come up, they’re new to me and they’re frightening because they’re deadly.

People talk about vaccines being a victim of their own success. People are not worried. They say, ‘What’s the big deal with measles?’ But measles kills one out of a thousand people, so I don’t want it.

DPM: So tell us a little bit about viruses in general. What is a virus?

SC: Viruses are incredibly simple. They’re a piece of genetic information surrounded by a protective protein shell. Some viruses also have a lipid membrane on top of that. Viruses can have few as 12 genes. And that’s it. So they can’t live on their own, they don’t have a metabolism, they’re just a delivery system for some genetic information.

But they have evolved. Viruses rapidly adapt to the environment because they replicate quickly. When they copy their genetic information, they make a lot of mistakes, so lots of viruses have a high mutation rate. That’s a perfect environment for adapting because they’re making a lot of progeny, and those progeny are genetically diverse. Natural selection picks the virus that is most successful. That’s why we see viruses that become resistant to drugs, for example.

DPM: So it’s not really a living organism? Intuitively, that doesn’t make sense.

A virus has genetic information, it can evolve, it can adapt and pick up mutations, so it seems like it has to be alive. But it has no metabolism, and it doesn’t grow in size like every living organism. So I fall on the side of they’re not alive.

SC: I know. In my biology class, I ask, ‘Are viruses alive or not?’ And then we have the debate, and I tell them it doesn’t really matter which side of the debate you come down on. It’s just a good way to define what life is.

A virus has genetic information, it can evolve, it can adapt and pick up mutations, so it seems like it has to be alive. But it has no metabolism, and it doesn’t grow in size like every living organism out there that grows in size and has the ability to take in energy and do work. Viruses have to infect a cell before they can do any of that.

So I fall on the side of they’re not alive, but if someone wanted to say they were alive, I’m not going to argue very strongly against that.

DPM: And they’re obviously more parasitic than anything.

SC: Yes, they are. We call them obligate intracellular parasites.

DPM: You might not have an answer for this, but why do they exist? Why did they come into being? Are they proto-life at the most ancient and basic level?

SC: Since they are parasites, life would have to have existed before them, but probably not for very long before them. Everything that’s alive gets infected by viruses—plants, even bacteria. So why do they exist? It’s because they can, because they do. There’s no advantage to having viruses, really.

DPM: How does a vaccine destroy a virus or prevent it from replicating?

The way the immune system works is you have a few immediate responses when you get infected, but then you have this very strong and very specific response that we call the adaptive immune response. So when you get vaccinated, you set up that adaptive immune response so that you’re ready for the next time you confront that exact same pathogen.

SC: Vaccines are designed to train your immune system to recognize the virus when you come in contact with it. The way the immune system works is you have a few immediate responses when you get infected, but then you have this very strong and very specific response that we call the adaptive immune response. But that takes up to couple of weeks to develop.

So when you get vaccinated, you set up that adaptive immune response so that you’re ready for the next time you confront that exact same pathogen. The goal of the vaccine is to train your immune system to be able to recognize the virus or the bacteria when you do come in contact with it.

DPM: And then what happens? Your immune system doesn’t allow it to invade your cells?

SC: Yeah. What happens is you have cells in your body called B cells and T cells. These cells get activated. For example, you get the measles vaccine, and it alerts the cells in your body that this is a foreign pathogen that you should be worried about.

Your B cells and T cells that are able to recognize that pathogen get activated, and your body creates more of them. When you actually do encounter a measles virus, those B cells and T cells that were previously activated are ready to respond immediately. You don’t have to wait a week to get a response.

The B cells make antibodies that will bind to the measles virus. So if I actually inhale a measles virus, my B cells will spit out antibodies that will bind to that measles virus and prevent it from infecting me.

If you just keep your hands washed and don’t touch your face, you should be in good shape.

DPM: What should you do to prevent infection from the coronavirus?

SC: Hand-washing and not touching your face. This virus can be spread through respiratory droplets an infected person might spread if they sneeze or cough, or a little bit of spit comes out of their mouth when they’re talking to you.

Potentially you could also become infected if that person sneezes, and the droplets get on the table and then you come by and touch that table and then touch your face. So if you just keep your hands washed and don’t touch your face, you should be in good shape. It’s the stuff you want to do in flu season anyway.